Biological Invasions

Díaz Cando, Patricia Elizabeth; Sonkoly, Judit; Fenesi, Annamária; Guallichico Suntaxi, Luis Roberto; Kovacsics-Vári, Gergely; Di Vita, Luca; Espinoza Ami, Francis David; Madar, Szilvia; Károlyi, Evelin; McIntosh-Buday, Andrea; Törő-Szijgyártó, Viktória; Tóthmérész, Béla; Török, Péter

doi: 10.1007/s10530-025-03748-5pmid: N/A

Sporobolus cryptandrus, a North American C4 grass, has recently invaded European sandy grasslands, particularly in Central Europe (Hungary), where it threatens native plant communities. As allelopathy has been documented for other Sporobolus species, we tested whether litter from S. cryptandrus has a different effect on the germination and seedling emergence of native grassland species compared to native grass litter. We examined nine native grassland species and S. cryptandrus under three treatments: no litter (control), native litter and S. cryptandrus litter. We hypothesized the followings: (i) Litter addition can hinder germination compared to no-litter control because litter imposes physicochemical barriers. (ii) Following the Novel Weapons Hypothesis, Sporobolus litter may exert a stronger negative effect on native species than native grass litter. (iii) Litter effects are likely species-specific due to interspecific differences in traits and sensitivity to microenvironmental changes. Litter presence did not have a consistent negative effect across species, Sporobolus litter negatively affected germination only in Bromus tectorum. For most other species, the effects of native and Sporobolus litter were highly similar, suggesting that Sporobolus litter did not introduce physicochemical characteristics sufficiently different from native litter to produce distinct effects on native species. However, the suppression of B. tectorum germination by Sporobolus litter may indicate potential allelopathic effects. These findings suggest species-specific litter effects and highlight that Sporobolus litter could offer novel insights for managing B. tectorum, a problematic invader in North America. Future research should explore the long-term effects of Sporobolus litter in guiding restoration actions and invasive species management.

Dietschler, Nicholas J.; Liu, Fangzhou; Celis, Sabrina L.; Whitmore, Mark C.; Agrawal, Anurag A.

doi: 10.1007/s10530-025-03739-6pmid: N/A

Understanding natural enemy communities in the native range of pest insects is critical for implementing management decisions where such pests are invasive. The hemlock woolly adelgid (HWA) is a destructive invasive insect, causing decline of hemlock forests in eastern North America. We studied patterns of predator coexistence and prey suppression among native predators in western North America to inform biological control strategies in the invaded eastern range. In particular, we examined the structure and interactions of HWA’s specialist predator complex (a beetle Laricobius nigrinus, and two flies Leucotaraxis argenticollis and Le. piniperda) across five western populations over two years. Field surveys quantified spatial and temporal overlap, while a laboratory experiment assessed competition between the two Leucotaraxis species. We employed species-specific RT-qPCR to quantify populations of cryptic Leucotaraxis immatures. Supporting the notion of complementary predation, predators exhibited clear temporal and spatial niche partitioning: (1) the two Leucotaraxis species were temporally separated, (2) while La. nigrinus overlapped with both Leucotaraxis species, they showed negative spatial co-occurrence on twigs, and (3) no evidence of competition between Leucotaraxis species was observed in the lab. These native predators appear to partition resources facilitating prey suppression, and they may be complementary in biological control. Nonetheless, during our study we observed only one HWA pest generation annually in the native western range, contrasting with bivoltine populations in the invaded east. This difference in pest voltinism, along with climatic differences between native and invaded communities, will likely influence predator–prey synchrony as the natural enemy complex establishes in invaded range.

Demian, Sarah; Anderson, Aidan; Braithwaite, Jaylene; Mckenna, Lauren; Clements, David R.

doi: 10.1007/s10530-025-03740-zpmid: N/A

Reynoutria spp. (the knotweed species complex) constitutes one of the most invasive plant taxa globally. Reynoutria spp. dispersal mechanisms facilitate rapid spread along watercourses. The 100-year Pacific Northwest flood of November 2021 impacted British Columbia’s Vedder-Chilliwack River and its biota through historically high rates of discharge, formation of new islands in the river, and removal of existing vegetation. According to our field surveys, a five-fold increase of Reynoutria patches was observed in 2022 along the Vedder-Chilliwack River as compared to 2019 with much of the increase observed in newly available disturbed areas created by the 2021 flood. Reynoutria patches in the river’s tributaries tended to be well-established whereas the age distribution in the mainstem was skewed towards younger age intervals, indicating tributaries may act as a major source of population growth if not controlled. Reynoutria patch numbers continued to expand, with 21% more patches in 2024 than in 2022 followed by a 97% increase in 2025 relative to 2024. The near doubling of the Reynoutria population in 2025 was likely connected to a significant rainfall event in October 2024. The number of patches in 2025 was nearly 12 times the number in 2019. Both the 2021 and 2024 flooding events are consistent with the global increase in flooding frequency and intensity due to climate change. Such flooding events can significantly contribute to the expansion of invasive plant populations on watercourses, highlighting the crucial need for targeted management in river systems to mitigate further spread across watersheds.

Hagh-Doust, Niloufar; Hakimzadeh, Ali; Kupagme, John Yangyuoru; Dierickx, Glen; Copoț, Ovidiu; Mikryukov, Vladimir; Tedersoo, Leho

doi: 10.1007/s10530-025-03741-ypmid: N/A

The recent pandemic, pathogen outbreaks, and devastating effects of invasive species in natural environments highlight the importance of global movements of organisms. Humans have facilitated global transport and the introduction of alien species via direct and indirect pathways. However, the complexities and possible dangers of the global transmission of microorganisms are not fully understood. Human footwear can be a potential vector for transmitting pathogenic and invasive microorganisms. Here, we investigated the biosecurity risks associated with the footwear of passengers arriving from various countries at Tallinn International Airport, Tallinn, Estonia. We collected dust or soil samples from passengers’ footwear and characterised the fungal and bacterial communities using metabarcoding. To evaluate potential risks to human and ecosystem health, we cross-referenced detected OTUs with the World Health Organization (WHO) priority pathogen lists and other curated fungal and bacterial databases. Our results suggested that the alpha diversity of fungal and bacterial OTUs carried by passengers’ footwear was not affected by geographical region or season. Whether the passenger had soil or dust on their footwear also had no significant effect on bacterial and fungal alpha diversity. Furthermore, our results showed that passengers’ footwear poses a biosecurity risk by transporting various types of pathogens, including plant and animal pathogens, as well as mycoparasites. Several types of bacterial and fungal human pathogens were also transported to the destination airport, among which many belonged to high-priority and critical risk groups defined by the WHO. The majority of the bacterial and fungal OTUs transferred by passengers’ footwear had not previously been reported from Estonia, which raises concern about their potential to become invasive in the future. Our results highlight the need to establish biosecurity measures in European airports. Further investigations are needed to assess the relationships between country-level factors and the potential biosecurity risks posed by passengers arriving from different countries.

Hardwick, James; Hackney, Christopher; Law, Alan; Pattison, Zarah

doi: 10.1007/s10530-025-03721-2pmid: N/A

Invasive Non-Native Plant species (INNPs) establishment along rivers continues to accelerate globally, with potential consequences for riverbank stability, ecosystem functions and services. Riverbank stability is dependent on the balance between destabilising forces (e.g., shear stress) and stabilising influences (e.g., sediment cohesion and native vegetation reinforcement). However, disturbance driven INNPs invasions are attributed to decreasing riverbank stability through outcompeting and replacing native vegetation. One such INNPs, Impatiens glandulifera (Himalayan Balsam), has been linked to increased riverbank erosion over winter owing to an annual post summer phenological dieback. Yet the impact of I. glandulifera on riverbank stability remains unknown. Here we show that I. glandulifera invasion indirectly amplifies seasonal reductions in riverbank shear strength. We found, using piecewise Structural Equation Modelling, that previous summer I. glandulifera cover indirectly influences riverbank shear strength via suppression of overwinter native vegetation cover, promoting the formation of bare ground. Riverbank shear strength was ~ 30% lower over winter in invaded compared to uninvaded sites. Our results demonstrate how an annual INNPs can amplify expected seasonal decreases in riverbank stability because of a seasonal phenological feedback. INNPs influence on riverbank stability has key implications for ecosystem function and services. As invaded riverbanks may be more vulnerable to erosion leading to morphological changes and downstream habitat degradation from increased sediment loading. Furthermore, these findings have management implications with potentially additional intervention measures required to mitigate reduced riverbank stability during INNPs removal activities.

Hoblyn, Ashley; Aldridge, David C.

doi: 10.1007/s10530-025-03735-wpmid: N/A

Groundwater-dominated streams support distinct biota and have significant conservation value. They include some of the most vulnerable freshwater habitats and are increasingly threatened by the invasion of signal crayfish (Pacifastacus leniusculus), a major driver of biodiversity loss in freshwater systems. This study aimed to assess the density-dependent impacts of signal crayfish on macroinvertebrate and macrophyte community dynamics in the River Shep, a UK chalk spring-fed stream. We conducted a four-week enclosure-exclosure experiment with four replicated treatments: two set signal crayfish densities (6 and 28 crayfish m−2), a crayfish exclosure and an open water control. We evaluated their impacts on macroinvertebrate abundance, diversity, and community composition, as well as on macrophyte cover, diversity, and community composition. Macroinvertebrate diversity was significantly higher in the exclosure treatments compared to the control and high and low crayfish density enclosures. However, no measurable impact of signal crayfish was observed on macrophytes nor on invertebrate abundance and community structures. These findings indicate that higher densities of signal crayfish negatively impacted macroinvertebrate diversity, while macrophyte communities were unaffected, suggesting that the ecological responses of groundwater-fed streams to signal crayfish invasions may differ from the responses of other stream environments. This study provides critical insights into the density-dependent ecological consequences of invasive non-native species in groundwater-fed streams. Our findings underscore the need for targeted management strategies that acknowledge the distinct processes of different freshwater systems, rather than applying broad, generalised management schemes that overlook the unique interactions and sensitivities specific to these ecosystems.

Prie, Vincent; Clement, Luc; Gaboriaud, Coline; Gailledrat, Miguel; Naudon, David; Bourru, Rémi; Lopes-Lima, Manuel; Valentini, Alice

doi: 10.1007/s10530-025-03750-xpmid: N/A

Environmental DNA (eDNA) is a powerful, non-invasive tool for detecting invasive species at an early stage, even when populations are small or elusive. Its high sensitivity can reveal introductions that might otherwise go unnoticed for decades. Large-scale eDNA surveys of freshwater bivalves across French rivers uncovered the presence of Unio carneus, a mussel species endemic to the Drin Basin in the Balkans and threatened in its native range. Identification was confirmed through genetic analysis of live specimens. In France, the distribution of U. carneus largely overlaps with that of the Albanian roach Pachychilon pictum, a fish introduced from the same region in the late 1980s, suggesting introduction via parasitic larvae on its host. However, detections outside the fish’s known range raise questions about alternative hosts and the mussel’s ability to adapt to local conditions. The French population shows low genetic diversity, consistent with a founder effect, and appears to be of low invasiveness to date. This case illustrates the value of eDNA for uncovering overlooked introductions and highlights the conservation paradox posed by species that are threatened in their native range yet may act as emerging invaders elsewhere.

Kishinevsky, Miriam; Ferrer-Suay, Mar; Ives, Anthony R.

doi: 10.1007/s10530-025-03731-0pmid: N/A

The enemy release hypothesis—that the success of invading species is due to release from natural enemies that occur in their home range but not in the new range—can be an important explanation for successful invasions. Testing this hypothesis is difficult, however, because testing requires documented cases of not only successful but also unsuccessful invasions. Therefore, observational data on after-the-fact establishment following unintentional introductions is insufficient, because they only include successful invasions. Here, we investigate the role of enemy release for parasitoid biological control agents and their hyperparasitoid natural enemies. We created a dataset of all parasitoid wasp species attacking aphids that were introduced into North America, including data on their hyperparasitoid species in the native and new range. In total, information on 29 species of primary parasitoids and 54 species of hyperparasitoids was obtained, combining to create 259 parasitoid-hyperparasitoid species associations. Results show that introduced parasitoids experience partial enemy release, but the degree of enemy release does not affect the chance of successful establishment or successful control. This lack of effect of enemy release might be due to the broad geographical range of the hyperparasitoids (perhaps from unintentional introductions) which reduces the degree of enemy release. In addition, the life-history traits of the hyperparasitoid communities in the new range were different from the native range, with relatively more generalist hyperparasitoid species in the new range. These results show that introduced natural enemies can experience enemy release, but that this does not necessarily help to predict their successful establishment.

Ziller, Sílvia Renate; da Rosa, Clarissa Alves; Sühs, Rafael Barbizan; Puechagut, Patricia Beatriz; Marterer, Beloni Terezinha Pauli; Silva, Carlos Henrique Targino; Legracie‐Júnior, José Renato; Chapla, Tatiani Elisa; Zenni, Rafael Dudeque

doi: 10.1007/s10530-026-03755-0

Macêdo, Rafael L.; Rickowski, Fiona S.; Jeschke, Jonathan M.; Rocha, Odete

doi: 10.1007/s10530-025-03726-xpmid: N/A

Contextualizing the lag between detection and publication of invasive species records is critical for management and communication. Using a literature review of records spanning 1963–2023 and complementary snapshot monitoring data (2012–2016), we quantify the lag time of reporting new records by researchers and illustrate the importance of timely and more reliable tracking of Ceratium spread, a genus of bloom-forming dinoflagellates with phytosanitary and ecological impacts. Our literature review indicates that records of C. furcoides and C. hirundinella (in South America) show considerable publication delays (C. furcoides 4.3 ± 2.6 years and C. hirundinella 4.9 ± 3.9 years), limiting early control and informed water management decisions. Our mixed-effects model revealed that publication delays have significantly decreased over time, but remain longer in Brazilian records and in reservoir and river environments. From monitoring data, C. furcoides was found at 72 sites, 53 of which remain unpublished to date, spanning urban, peri-urban, and rural water bodies in São Paulo, South America’s most populous state. The species was absent from 225 sites, often associated with slightly higher water quality and preserved vegetation. More transparent and timely reporting, including absence data, is essential to enable risk modeling and preventive planning in a changing world. Once published, such data can offer valuable insights into species distributions, enabling reconstruction of invasion routes, estimation of spread rates, and identification of potential lag phases.